Question: My Mum, sister and I, all get migraines. What makes our vision funny?

Ed Bracey answered on 14 Nov 2017:

Hi Tom,
Interesting question!
I’m doing a collaboration with a performing artist who gets these too.
We’re still not completely sure what causes them.
What seems to cause the visual symptoms is something called a cortical spreading depression.
Your visual cortex is the part at the back of the brain that receives information about vision.
Everything you see is mapped out there on the surface of the brain.
In a migraine, the cells in the visual cortex become hyperactive, and after that burst of activity, they get tired out, or “depressed”.
So it’s a depression of the cortex, or “cortical depression”.
It starts in a small area of the visual cortex and so only affects a small amount of your “visual map” at first, and then spreads across the visual cortex in a wave, making the funny vision spread. So that makes is a cortical spreading depression.
If the visual symptoms look like they do in this video:

then you can see that there’s a strange sparkly light at the start – that’s caused by the front of the wave of activity when the brain cells in your visual field are hyperactive. The grey/blurred part that follows it is caused by the depression, where the cells are then tired.
This makes those parts of your visual cortex stop working so well, so things appear dull or blurred.
As you can see, it normally starts in a small area and then spreads to affect more and more of the vision.
We’re still not entirely sure about what triggers these things to start.

With my artist friend, we created an augmented reality version of this, using google cardboard and smart phones, so other people can understand how annoying it is!